The present invention relates to simulators, and more particularly, to a simulator simulating the ignition system of an automobile engine and which may be used in the calibration of automobile repair and maintenance equipment.
Engine scope testers have provided the modern mechanic with a powerful tool for accurately setting the ignition system of, and checking the performance of, an engine. Input leads from the scope tester are connected to various points in the ignition system to sense the electrical signals passing therethrough. Additionally, output leads are connected from the engine scope tester to the ignition system to allow the scope tester to control and override functions of the ignition system when making certain tests. Typically, one input lead to the scope tester is connected to sense the firing of the sparkplug in the cylinder designated as #1. This lead is used to trigger a tachometer indicating the engine speed in RPM on a meter on the scope tester. Additionally, this lead is used to trigger the sweep of a CRT display on the scope tester. The CRT display has a calibrated scale for the performance comparison and measurement of the various waveforms displayed thereon.
A second lead is connected to sense the high voltage lead from the coil to the center terminal on the distributor cap. A high voltage pulse passes through this lead every time a sparkplug in the engine fires. This lead is used to vertically deflect the sweep on the CRT display to give a visual representation to the ignition system under test. In one mode of operation, the engine scope tester spans the CRT display from side to side with one complete firing sequence of the engine, beginning and ending on cylinder #1. In another mode of operation, the engine scope tester displays a selected cylinder's ignition pulse across the entire CRT display. A properly operating ignition coil causes a distinctive "ringing" output on the CRT which is readily apparent to a trained mechanic. Various other display modes are also provided which allow the mechanic to measure ignition system voltages, point "dwell" and the like against the calibration markings on the CRT.
Additionally, as mentioned above, the engine scope tester is capable of controlling the ignition system to enable the mechanic to perform certain tests on the engine itself using the scope tester. A pair of leads is connected across the primary of the ignition coil under control of the engine scope tester. In normal operation, a high voltage pulse is generated in the coil by first closing the electrical path through the primary of the coil to establish a magnetic fluid. The circuit through the primary is then opened to allow the magnetic field to collapse and, thereby, induce a high voltage in the secondary of the coil. The circuit through the primary is controlled by the ignition breaker points. If the leads from the engine scope tester, being in parallel with the breaker points, maintain the circuit through the primary when the breaker points open, the firing of the sparkplug which would have fired at the time of breaker point opening can be suppressed. Since the engine scope tester is provided with an indication of the firing sequence through the input sensing the cylinder #1 lead, it can calculate the time of firing of any or all cylinders and suppress the firing of the associated sparkplug(s) by the above process. In a perfectly balanced engine in which all cylinders are contributing to the total running efficiency, the suppressing of the firing of one or more sparkplugs should have a proportional effect on the performance of the engine as measured in RPM by the tachometer on the engine scope tester. When testing the engine, the mechanic uses the engine scope tester to bypass the firing of selected cylinders. A cylinder having poor valves, rings, or the like will have a disproportionate effect on the engine speed recognizable by a trained mechanic.
Whenever an engine scope tester is repaired, tested for accuracy, or calibrated, a simulator of some sort which simulates an automobile engine's ignition system in a manner which will provide the required outputs needed as inputs by the engine scope tester, at known accurate rates, must be employed. Further, the simulator must respond to the feedback outputs of the engine scope tester to check if they are properly working and able to suppress selected sparkplug firings by an ignition system. Typically, the foregoing functions involve the use of a motor driven distributor connected to a number of spark plugs. In other words, the normal components of an automobile engine ignition system are artificially driven with a motor and connected to an appropriate DC power source, be it rectified AC or an actual lead storage automobile battery. Such mechanical devices have a number of disadvantages, not the least of which is their size and noise. They do not respond completely to the feedback of the engine scope tester. Moreover, they do not combine both a simulator and a calibrator into a single unit. Additionally, separate provision must be made for 8 cylinder, 6 cylinder, 4 cylinder, and rotary engines.
It is an object of the present invention, therefore, to provide an engine scope tester calibrator of solid state construction, providng outputs and inputs of known accuracy and faithfully duplicating the performance of an engine ignition system for an engine scope tester to interface with when testing and calibrating apparatus and functions such as a tachometer, dwell, voltage measurements, sparkplug firing suppression and a timing light. Such apparatus also should be capable of appearing as an 8 cylinder engine or as a 6 cylinder, 4 cylinder or rotary engine.